A number of techniques exist for Non-Destructive Testing (NDT) of components for the presence of surface cracks. Some observation based techniques employ, for example, ultrasonic or radiographic inspection. Other techniques, such as eddy current methods, use material response characteristics to indicate the presence of flaws.
It is generally accepted that NDT methods that can be performed in situ are preferable as this can avoid the need to take the equipment “off line”, thus avoiding down time of the equipment and component to be tested. One in situ method for testing for the presence of surface cracks in a component involves establishing a pressure differential between at least two enclosed regions on the surface of the component. A surface crack of sufficient size that extends between two regions of differential pressure will cause a flow of air through the crack from the region of higher pressure towards the region of lower pressure. Monitoring for such a flow of air can be indicative of the presence of a surface flaw.
International Patent Application No. PCT/AU01/00504 (filed by the present applicant) discloses a system for monitoring the integrity of a structure. The system includes a sensor pad having a surface, which is sealed onto the surface of the structure to monitor for the presence of a flaw (such as a crack) within the structure and opening onto the surface.